Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The readOnlyHint annotation already establishes safety, but the description adds meaningful behavioral detail beyond that: the newest-first ordering, the exact API path, the pagination envelope ({ data, pagination } when more pages exist), and the full set of returned fields. This transparency is strong given the simple read-only nature of the tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences front-load the core purpose and ordering, then deliver the endpoint and return format without filler. The field enumeration is dense but directly useful since there is no output schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description fully specifies what the tool returns: the invoice object fields and the pagination wrapper. Combined with the schema's exhaustive parameter descriptions and the readOnlyHint annotation, an agent has everything needed to invoke the tool correctly and interpret its results.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, and every one of the seven parameters already has a clear, specific description with formats, enums, defaults, and pagination semantics. The phrase 'optional filters' in the tool description adds no parameter-specific meaning beyond what the schema provides, so the baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb, resource, and ordering: 'List invoices, newest first, with optional filters.' It also names the underlying API endpoint (GET /invoices) and enumerates the returned invoice object fields, making the tool's scope unambiguous among the many list_* siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description clearly conveys what the tool does and the context for using it (list invoices with optional filters, newest first). However, it does not explicitly contrast this with alternatives like get_invoice for single-record retrieval or create_invoice for writes, so it stops short of full exclusionary guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.